A virtual private network (VPN) is a private communications network often used within a company, or by several different companies or organizations, to communicate confidentially over a publicly accessible network.
VPN involves two parts: the protected or "inside" network, which provides physical and administrative security to protect the transmission; and a less trustworthy, "outside" network or segment (usually through the Internet). Generally, a firewall sits between a remote user's workstation or client and the host network or server. As the user's client establishes the communication with the firewall, the client may pass authentication data to an authentication service inside the perimeter. A known trusted person, sometimes only when using trusted devices, can be provided with appropriate security privileges to access resources not available to general users.